Fabrication of Nb/AlO/sub x//Nb tunnel junctions using focused ion beam implanted Nb patterning (FINP) technique

Abstract

We have applied the Focused ion beam Implanted Nb Patterning (FINP) technique to fabrication process of Nb/AlOx/Nb tunnel junctions. The essence of this technique is that Ga ion implanted layers in Nb films serve as a masking layer during reactive ion etching (RIE) in CF4 plasma. Uniform and reproducible patterns of 0.3 x 0.3 pm2 have been formed by this technique. The tunnel junction fabricated with a 60 keV ion beam had the quality parameter Vm of 48 mV, which indicates no degradation of junction characteristics by focused ion beam irradiation. We have also investigated the CF4 plasma etching characteristics of Ga ion implanted Nb films and have found that an improvement in the characteristics is achieved by lowering beam energy and raising CF4 gas pressure.